a) Field of the Invention
The invention is directed to a vacuum valve comprising a valve housing which has an inlet opening and an outlet opening penetrating opposite walls of the valve housing, a valve seat surrounding the inlet opening, a valve disk which is located in the interior space of the valve housing and is arranged on a carrying arm that is rigidly connected to a shaft which, for purposes of opening and closing the vacuum valve, is rotatable around its longitudinal axis and displaceable in axial direction, and a driving device by which the valve disk can be adjusted from a closed position, in which it is pressed against the valve seat, by way of an intermediate position, in which it is lifted from the valve seat, into an open position in which it releases the inlet opening by an axial displacement of the shaft, and the driving device comprises a rotary drive for rotating the shaft.
b) Description of the Related Art
Vacuum valves of the type mentioned above are also called pendulum valves and are known in various embodiment forms. A pendulum valve of this type is known, for example, from U.S. Pat. No. 6,776,394 B2. The rotatable sleeve which is displaceable in axial direction and at which the carrying arm carrying the valve disk is arranged is connected to the valve housing by a linked guide and an external thread of a shaft is screwed into an internal thread of the sleeve extending in axial direction of the sleeve. By rotating the shaft, the sleeve, in cooperation with the linkage guide, is displaced in axial direction and rotated so as to open and close the valve. Further, pistons are arranged in the cylinder spaces of the valve housing which lie around the outlet opening, the piston rods of the pistons being guided in the vacuum area of the valve and forming tappets which press the valve disk against the valve seat in the closed position of the valve disk. This increases the closing force that can be applied. But the closing force that can be applied by these pistons is limited due to their small dimensions. However, depending on the differential pressure acting on the valve disk and the size of the valve disk, comparatively large closing forces may be required which cannot be achieved in this construction under certain circumstances.
US 2004/0079915 A1 describes, among others, a vacuum valve in the form of a pendulum valve. In this case, a carrying plate carrying a valve plate and a supporting plate is arranged at the swivelable carrying arm. The valve plate and the supporting plate are adjustable relative to the carrying plate in axial direction of the inlet opening and outlet opening of the valve housing by means of piston-cylinder units. The sealed state of the vacuum valve is brought about in that the valve plate presses against the valve seat surrounding the inlet opening and the supporting plate presses against the valve housing in the area of the outlet opening. A plurality of pistons are provided in the piston spaces of the carrying plate for displacing the valve plate relative to the carrying plate. The construction of this vacuum valve is relatively uneconomical on the whole. The constructional variant in which the supporting plate is omitted is also mentioned. In this case, the closing force for pressing the valve plate against the valve seat must be transmitted via the carrying arm of the valve plate. Therefore, the closing force that can be applied is limited, or the carrying arm must be correspondingly massive.
U.S. Pat. No. 6,561,482 B2 also shows, among others, constructional variants in the form of pendulum valves. In this case, the valve plate is again held by a carrying plate fastened to the carrying arm, and the carrying plate is provided with a piston-cylinder unit, the valve plate being arranged at the piston rod thereof. The valve plate can be pressed against the valve seat by means of this piston. A bellows seal is arranged between the valve plate and the carrying plate, and openings which open into the space between the valve plate and carrying plate are provided in the valve plate. A pressure balance can be achieved between the two sides of the valve plate through these openings. The construction of this valve is uneconomical and the structural height in axial direction of the valve opening is relatively large. This publication further describes an embodiment form constructed as a slide valve in which a supporting plate is held at the valve plate by means of a piston-cylinder unit. In the sealed state of the valve, the supporting plate is pressed against the stops of the valve housing which are arranged in the area surrounding the outlet opening. The valve plate is accordingly pressed against the valve seat. In this case, the movement of the valve plate must be absorbed by a sufficient elasticity of the valve rod. Also, the closing force that can be applied is comparatively small, and differential pressures are again compensated by a bellows seal between the supporting plate and the openings opening into the space between the supporting plate and valve plate.